1. Field of the Invention
The present invention relates to a method for producing a Group III nitride semiconductor light-emitting device, which is characterized by a method for forming a p-type contact layer.
2. Background Art
Patent Documents 1 to 4 disclose that a p-type contact layer has a two-layer structure in which a first p-type contact layer and a second p-type contact layer are sequentially deposited on a light-emitting layer to reduce the contact resistance between the p-type contact layer and an electrode in a Group III nitride semiconductor light-emitting device.
For example, Patent Documents 1 to 3 disclose a light-emitting device that the first and second p-type contact layers are both formed of Mg-doped GaN, and the second p-type contact layer has a Mg concentration higher than that of the first p-type contact layer. Thus, when the Mg concentration of the second p-type contact layer being in contact with an electrode is higher than that of the first p-type contact layer, the contact resistance is reduced. When the Mg concentration of the first p-type contact layer is lower than that of the second p-type contact layer, the carrier concentration is increased.
Patent Document 1 discloses that the Mg concentration of the first p-type contact layer is 1×1020/cm3, and the Mg concentration of the second p-type contact layer is 2×1020/cm3. Moreover, Patent Document 1 discloses that hydrogen or nitrogen is employed as carrier gases for forming the first and second p-type contact layers, and that the first and second p-type contact layers are both formed at a temperature of 850° C.
Patent Document 2 discloses a light-emitting device in which the first p-type contact layer has a Mg concentration of 1×1019/cm3 to 1×1020/cm3, and the second p-type contact layer has a Mg concentration of 1×1020/cm3 to 1×1022/cm3. A mixture gas of nitrogen and hydrogen is employed as a carrier gas for forming the first p-type contact layer, and hydrogen is employed as a carrier gas for forming the second p-type contact layer. The first p-type contact layer is formed at a growth temperature of 900° C. to 1,050° C., and the second p-type contact layer is formed at a growth temperature of 800° C. to 1,050° C.
Patent Document 3 discloses that the first and second p-type contact layers are both formed at a growth temperature of 800° C. to 900° C.
Patent Document 4 discloses a light-emitting device in which the first p-type contact layer is formed of Mg-doped GaN, and the second p-type contact layer is formed of Mg-doped InGaN. Moreover, nitrogen is employed as a carrier gas for forming the second p-type contact layer. InGaN has a work function smaller than that of GaN, which is closer to a work function of electrode material. Therefore, when the second p-type contact layer being in contact with the electrode is formed of InGaN, the contact resistance therebetween can be reduced.
Patent Document 1: Japanese Patent Application Laid-Open (kokai) No. H8-97471
Patent Document 2: Japanese Patent Application Laid-Open (kokai) No. 2013-128055
Patent Document 3: Japanese Patent Application Laid-Open (kokai) No. 2010-87056
Patent Document 4: Japanese Patent Application Laid-Open (kokai) No. 2013-21173
However, the contact resistance was not sufficiently reduced by the method for forming the p-type contact layer having the conventional two-layer structure disclosed in the above Patent Documents 1 to 4. Therefore, further reduction of contact resistance was needed. When the second p-type contact layer is formed of InGaN, the light output is reduced although the contact resistance can be reduced. Therefore, the second p-type contact layer is preferably formed of GaN.